Harrison Nicholls / Curriculum Vitae

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My research explains observed exoplanetary properties and atmospheric compositions, while making predictions as to their histories and formation scenarios. This is undertaken through numerical modelling, which captures the physics active from planet formation up to the present day.

Employment and education

Research Associate in Exoplanet Modelling

University of Cambridge, United Kingdom
Feburary 2026 — 2029

Postdoc research associate working with Oli Shorttle at the Institute of Astronomy. Investigating the role of volatile chemistry, solubility, and gas radiative properties in controlling the observable characteristics of sub-Neptune/super-Earth exoplanets.

DPhil in Atmospheric Oceanic and Planetary Physics

University of Oxford, United Kingdom
October 2022 — January 2026

I developed numerical models to explore the evolution of rocky (exo)planets, providing new perspectives on how coupled interior-atmosphere interactions and their feedbacks shape planets over deep time. The PROTEUS framework has now become an established community modelling tool. Supervised by Ray Pierrehumbert and co-supervised by Tim Lichtenberg. Examined by Paolo Sossi and Tad Komacek, and awarded without corrections, my thesis is available below.

MPhys in Physics

University of Exeter, United Kingdom
September 2018 — July 2022

Four-year integrated MPhys Physics programme completed with a 1st (final grade of 85%). Modules included: astrophysics, electromagnetism, analytical dynamics, thermodynamics, scientific programming, and extensive partnered lab work. Supervised by Éric Hébrard; my dissertation was published in MNRAS as Nicholls+23.

Scientific publications

My first-author publications are listed below.
You can view a complete list of associated works on my NASA/ADS/SciX library.

What happened to rocky planets?

Nicholls (2026), DPhil Thesis
University of Oxford, doi:10.5287/ora-bmz5xpbrk, pdf:thesis.pdf

To explore the question of why rocky planets (in the Solar System and beyond) are observed to span such a wide diversity of climate states, I developed and applied the PROTEUS framework to directly simulate the multi-physical evolution of planets over their billion year histories. I highlight the key processes active during early magma ocean periods, including novel atmosphere-interior feedbacks and key climate physics. Applying my modelling to specific exoplanets bridges the gap between observational constraints from JWST and the hidden atmospheric/geological mechanisms which shape rocky worlds across the universe.

Volatile-rich evolution of molten super-Earth L 98-59 d

Nicholls, Lichtenberg, Chatterjee, Guimond, Pierrehumbert (2026)
Accepted in Nature Astronomy, arxiv:2507.02656

I study the evolution of the super-Earth L 98-59 d from its formation up to the present day. Including atmospheric escape alongside my real-gas atmosphere structure model, I reproduce JWST observations of its hybrid H2-H2S-SO2 atmosphere. These results indicate a volatile-rich and geochemically-reducing birth scenario, inviting a more nuanced classification framework for small planets beyond the 'water world' and 'gas dwarf' paradigms. Presented at Exoclimes VII and EPSC-DPS 2025.

Self-limited tidal heating and prolonged magma oceans in the L 98-59 system

Nicholls, Guimond, Hay, Chatterjee, Lichtenberg, Pierrehumbert (2025c)
Published in MNRAS, doi:10.1093/mnras/staf1167, arxiv:2505.03604

Observations of L 98-59 indicate that it hosts three planets with large orbital eccentricities. I calculate the tidal heating within these planets self-consistently with outgassing and atmospheric energy transport. A robust feedback between tidal heating, radiative cooling, and mantle rheology leads to self-regulation of tidal heating. Tidal heating may allow them remain molten for a long time, and raises the potential for 'tidally supported worlds'.

AGNI: A radiative-convective model for lava planet atmospheres

Nicholls, Pierrehumbert, Lichtenberg (2025b)
Published in JOSS, doi:10.21105/joss.07726, arxiv:2506.00091

Accurate models for the atmospheres of lava planets are critical for understanding their evolution and present states. I present a new radiative-convective real-gas atmosphere model for lava planets. This model is designed to be flexible and accurate, allowing for rapid exploration of parameter spaces while including a suite of physical processes.

Convective shutdown in the atmospheres of lava worlds

Nicholls, Pierrehumbert, Lichtenberg, Soucasse, Smeets (2025a)
Published in MNRAS, doi:10.1093/mnras/stae2772, arxiv:2412.11987

Using a new radiative-convective atmosphere model 'AGNI', I found that atmospheres on permanent lava worlds can be convectively stable. Absorption features of CO2 and SO2 within emission spectra are associated with mantle redox state. Presented at UKPF Meeting 2025.

Magma Ocean Evolution at Arbitrary Redox State

Nicholls, Lichtenberg, Bower, Pierrehumbert (2024)
Published in JGR Planets, doi:10.1029/2024JE008576, arxiv:2411.19137

With a new interior-atmosphere modelling framework 'PROTEUS', I simulated the evolution and cooling of primordial terrestrial magma oceans. The greenhouse effect of outgassed atmospheres exerts significant control over magma ocean cooling and crystallisation. Presented at EGU 2024.

Self-Consistent Modelling of Flares and Gas Giants

Nicholls, Hebrard, Venot, Drummond, Evans (2023)
Published in MNRAS, doi:10.1093/mnras/stad1734, arxiv:2306.03673

Using a radiative-convective photochemical kinetics model, I found that flares induce observable features in the spectra of sufficiently cool gas giants orbiting M-stars. Presented at Exoclimes VI.

Teaching and work experience

Reviewer for scientific journals

Winter 2024 — Ongoing
I have twice been a reviewer for PSJ, assessing research on atmospheric energy transport. I have also been a reviewer for A&A, for an article on planet formation chemistry.

Co-supervision of BSc project on tidal heating

Spring — Summer 2025, Groningen
Following the formation of the Moon, substantial amounts of tidal heat energy may have been dissipated within Earth. This project theoretically tested how such heating influenced early Earth and the onset of habitable conditions. The student used the PROTEUS framework that was largely developed during my PhD, and later worked as a research assistant. Their thesis is in review for publication and available on arXiv.

Co-supervision of BSc project on runaway greenhouse

Spring — Summer 2024, Groningen
This project aimed to test the robustness of the canonical runaway greenhouse effect, considering different secondary atmosphere compositions. We then worked to turn their thesis into a paper, published in ApJ. I guided the student through the research project, including the use of computer simulations and statistical analysis, and provided feedback and assessment of their dissertation at the end of the project.

Teaching electromagnetism in undergraduate labs

Autumn 2023 — Summer 2025, Oxford
Demonstrating electromagnetism lab experiments to undergraduate students at Oxford. The experiments involve calculating various physical constants, and demonstrating known relationships such as Faraday’s Law. Demonstrating in labs has taught me several skills, particularly on providing instructions and constructive feedback.

Primary school outreach programme

Autumn 2022, Oxford
I visited two primary schools to engage Year 5 children with workshops on general physics. Introduced a class of 30 to broader concepts, and then worked with groups to conduct small experiments.

Summer internship on photonic cavities

June 2020 — August 2020, Exeter
Using proprietary FDTD software and open source data science libraries, I optimised photonic crystal cavities for the desired characteristics. My code was later applied to other photonic systems by the research group at Exeter.

Summer internship at micro-LED company

June 2019 — August 2019
I was involved with the development of gallium nitride micro-LED display technology with the process engineering group. This included operation of plasma etch tools, as well as developing novel methods for colour conversion using quantum dots.

Awards

Programming skills